Light shutters, optical filters are commonly used in series with optical sensors to protect the sensors from be injured or jammed by light. Shutters include mechanically and electro-mechanically operated shutters. Optical filters include passive optical reflectors, passive narrow and broad band optical filters, and electro-active narrow and broad band filters. Sensors include cameras, detector arrays, and even human eyes. When the sensor is human eye, the light shutters or optical filters are commonly termed as protective eyewear.
Displays in series of prior-art switchable mirrors, and mechanically moveable mirrors are also reported. Displays include television, computer monitor, to name a few. The technologies for those prior-art switchable mirrors include Electrochromic (EC), Suspended particle devices (SPDs), Thermochromics (TC), and Reversible electrochemical mirror (REM).
Electrochromic (EC) material changes its opacity between a colored, translucent state (usually blue) and a transparent state under a burst of electricity, controlling the amount of light and heat passing through. No electricity is needed for maintaining the particular shade. Recent advances in EC materials pertaining to transition-metal hydride electrochromics have led to the development of reflective hydrides, which become reflective rather than absorbing, and thus switch states between transparent and mirror-like. For example, National Institute of Advanced Industrial Science and Technology (AIST), Japan, announced such kind film.1 However, its IR clear state transmittance is only limited to 38%. Moreover, it attenuates visible light significantly, up to 55%. Also, it takes long time to transition from one state to another, in several minutes. A typical mirror is developed by Lawrence Berkeley National Laboratory.2 EC based smart glazing are being developed by SAGE. 1 http:/www.aist.go.jp/aist_e/latest_research/2007/20071213/20071213.html2 “Sb—Cu—Li electrochromic minors”, Gao Liu, Thomas J. Richardson, Solar Energy Materials & Solar Cells 86 (2005) 113-121
Suspended particle devices (SPDs)3 consist of rod-like particles suspended in a fluid. Research Frontiers is the developer. Under zero voltage, the particles are arranged in random orientations and tend to absorb light. When voltage is applied, the particles align and let light pass. SPDs can be dimmed, and allow control of the amount of light and heat passing through. A constant electrical current is required to keep the SPD smart window in transparent stage. It limits only 51% transmittance in clear state. 3 http://www.businesswire.com/portal/site/google/?ndmViewId=news&newsId=20090611006077&newsLang=en
Thermochromics (TC) material changes color with temperature. RavenBrick4 has developed a new TC material. It darkens in response to an increase in the temperature of the window without an electric current or human intervention. Unfortunately, its clear state transmittance is only around 40%. 4 http://www.ravenbrick.com/
Reversible electrochemical mirror (REM),5 as developed by Rockwell Scientific, is based on reversible electro-plating deposition of silver (Ag+/Ag). Via applying DC voltage, a layer of silver can be deposited onto the inner surface of glass substrate to form a reflective mirror to reject sunlight and heat. Under a reverse DC voltage which dissolves the silver layer, the mirror becomes transparent allowing solar heating through the window. 5“Efficient Adjustable Reflectivity Smart Window”, Morgan Tench, http://www.govforums.org/e&w/documents/Rockwell.pdf
U.S. Pat. No. 6,674,505 which is incorporated by reference in its entirety which discloses a device and method of manufacturing a single layer multi-state ultra-fast cholesteric liquid crystal (CLC) includes two optically transparent states with a liquid crystal arranged therebetween, and changing the optical states of the liquid crystal ranging from one state to any combination of broadband reflection, tunable narrow band reflection, light scattering, and transparency in accordance with a voltage applied to the device. A surfactant can be added to reduce the response time and a dichroic dye may be added to include the property of light absorption and reduce the bandwidth. The device can provide any and all of the aforementioned optical states for infrared light, visible light, and ultra-violet light. The desired outputs can be formed according to need, so that predetermined optical states can operate with either no voltage or a particular voltage or voltage range.